Impacts of starvation on male reproductive success in Tribolium castaneum

Background: Starvation is known to decrease male reproductive success in Tribolium castaneum. Starved males transfer less sperm, but we do not know whether reduced reproductive success is caused by lower oviposition rates of females or more frequent deposition of unfertilized eggs. Study organism: The red flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae). Questions: Does the nutritional state of a male influence female oviposition rate and/or fertilization capability? Does sperm use by females at fertilization reflect reduced numbers of sperm transferred by starved males? Hypothesis: If the number of sperm released by females reflects the number of sperm stored, we would expect the number of sperm per egg to be inferior if mated with starved males. Methods: We assessed female oviposition rate and fertilization capability in females mated with fed versus starved males. We also quantified sperm use via microscopical counts of DAPI-stained sperm heads on freshly deposited eggs. Results: Females mated with starved males were less likely to deposit eggs and deposited fewer eggs. Furthermore, the eggs of females mated with starved males had fewer sperm, and those females laid a significantly higher proportion of unfertilized eggs. Based on our counts of sperm per egg, we estimate that for starved males, about a third less sperm come close to the site of fertilization.